1. Field of the Invention
The invention is related to coding mode control in cellular telecommunication systems. Particularly, the invention is directed to a method for selection of the coding mode for a multi rate connection between a mobile station and a digital cellular telecommunication network.
2. Description of the Related Art
The following list defines some of the abbreviations used in this specification:
ACadmission controlAMRadaptive multi rateBSbase stationBTSbase transceiver stationCDMAcode division multiple accessC/Icarrier to interference ratioFERframe error rateGSMgeneral system for mobile communicationsLCload controlMACmedium access controlRMradio resource managerRRCradio resource controlRRMradio resource managementRNCradio network controllerSHOsoft handoverTCtranscoderTFtransport formatTFCtransport format combinationTFCItransport format combination identifierTFCStransport format combination setUEuser equipmentUMTSuniversal mobile telecommunication systemUTRANUMTS terrestrial radio access networkWCDMAwideband CDMA
The AMR concept provides a multi rate capability for connections between a mobile station (MS, also referred to as ‘user equipment’—UE) and a network. The AMR speech codec has 8 different bit rates (from 4.75 kbps to 12.2 kbps) for speech coding. A higher bit rate provides better speech quality but gives lower capacity and coverage. In GSM, the AMR control is a link level control function, controlled by the BTS and based on C/I measurements. In GSM, the codec mode control is in the BTS. For control of downlink direction, the mobile station (MS) reports observed C/I to the BTS. For control of uplink direction, the BTS measures C/I.
The present specifications of the WCDMA system leave room for improvement of the usage of the AMR concept because they do not describe adequate methods to optimize transmission control with the AMR concept. Thus, there is a need for methods of optimizing transmission control when using AMR connections.